In some years' time, at least four independent, but interoperable global satellite navigation systems (GNSS—global navigation satellite systems) will be available: Galileo, GPS III, GLONASS and COMPASS. Said new and modernized systems will provide new signals and services. It will be the first time that open-service signals (free-service signals) will be globally available on more than one frequency band. The performance of receivers will be improved by using multi-band navigation.
For example, increased accuracy may be achieved. Multi-band reception enables measuring and removing the ionospheric error. The new wide-band signals, above all Galileo E5 having a bandwidth of more than 72 MHz, promise to provide exceptional multi-path stability and increased tracking accuracy.
Likewise, availability may be increased. Interoperability between all GNSS systems increases the availability of space vehicles from currently 24 GPS Naystar and a few GLONASS to more than 100 space vehicles with additional Galileo and COMPASS satellites. Both the service availability, e.g. in street canyons, and the dilution of precision (DOP) and, thus, positional accuracy may be improved.
In addition, robustness may be increased. If a signal band exhibits a malfunction, it will still be possible to use a different one.
Moreover, integrity may be improved. Galileo will provide integrity data within the context of its service for the protection of human life in the I/NAV type of messages, which is broadcast via E5b-1 and E1-B (see “Galileo Open Service Signal in Space Interface Control Document (OS SIS ICD), Draft 1, “techn. rep., European Space Agency/European GNSS Supervisory Authority, February 2008”). This service is crucial for many applications relevant to security.
Once said new GNSS signals are available, several new or improved applications will become possible due to the advantages mentioned above, particularly in the mass market sector. However, mass market applications may use small, low-power and low-cost receiver devices. This is why an integrated approach is desired.
Front-end receivers (input component of a receiver) for said new and almost any wide-band signals are already available, but mostly consist of large, expensive discrete approaches for professional high-end applications which have high power consumption. First integrated multi-band front-end solutions are available now but leave room for improvement.
Four different approaches for multi-band receivers are common today.
For special applications such as GNSS reference receivers, there are the discrete high-end front-ends (or input components of the upper performance category, see, e.g., “F. Foerster, A. Carrera, N. Lucas and G. Rohmer, “High Performance Receiver Front-End for Multiple Galileo Frequencies”, in Proceedings of the 18th International Technical Meeting of the Satellite Division of the Institute of Navigation ION GNSS 2005, pp. 935-940, September 2005”). Said front-ends provide maximum accuracy, but are not suited for the application intended due to their high price, their very high power consumption and their size.
Through the progress made in the field of high-performance analog-to-digital converters (ADC), RF (radio frequency) or sub-sampling ADC front-ends are becoming increasingly attractive also for wide-band signals (see “A. Alonso, J.-M. Perre, and I. Arizaga, “A Direct Sampling Digital Receiver For Multiple GNSS Signals”, in Proc. of ENC-GNSS 2008, 2008”, “E: R. Parada, F. Chastellain, C. Botteron, Y. Tawk, and P.-A. Farine, “Design of a GPS and Galileo Multi-Frequency Front-End”, in IEEE 69th Vehicular Technology Conference: VTC2009-Spring 26-29 Apr. 2009, Barcelona, Spain, 20092”). The desired signals are filtered and subsequently down-converted while using intentional aliasing in analog-to-digital conversion. This type of architecture may use an extremely low-jitter clock as well as an ADC having a high analog input frequency bandwidth. The sub-sampling architecture exhibits high power consumption in the front-end and also in subsequent digital baseband signal processing. Generally, this architecture suffers from interferences, aliasing of out-of-band noise in the IF (intermediate frequency) range, and potential instability due to the high gain needed within one frequency range. Therefore, the sub-sampling architecture is not suited for an integrated receiver of the advanced mass market.
Another way multi-band reception can be provided is by using separate single-frequency front-ends for each desired GNSS signal or by integrating several more or less stand-alone receivers on one single chip (see “Z. Gradincic, “Multi-band GNSS Receiver,” 2007. US 20070096980 A1”). This is the straightforward way, but it suffers from home-made interferences through the different frequency synthesizers needed and is not an economic or optimized solution in terms of power consumption and size.
Other fully integrated multi-band front-end architecture solutions proposed in “M. Detratti, E. Lopez, E. Perez, and R. Palacio, “Dual-Band RF Front-End Solution for Hybrid Galileo/GPS Mass Market Receivers,” in Consumer Communications and Networking Conference, 2008. CCNC 2008, 5th IEEE, pp. 603-607, January 2008” and “J. Ko, J. Kim, S. Cho, and K. Lee, “A 19-mW 2.6 mm2L1/I2 dual-band CMOS GPS receiver,” Solid-State Circuits, IEEE Journal of, vol. 40, pp. 1414-1425, July 2005” use a switch for band selection. Therefore, they can only receive one single band at a time, thus eliminating the advantages of simultaneous multi-frequency GNSS processing or ionospheric correction.
An example of a multi-frequency band receiver is also shown by the published application DE 102008026698 A1. The multi-frequency band receiver described includes a first path configured to process a first frequency band and a second frequency band, and a second path configured to process a third frequency band. The first frequency band and the second frequency band have a smaller distance than the first and the third as well as the second and the third frequency bands.